An optical microphone converts acoustic pressure waves into electrical signals by detecting light beams, instead of sensing changes in capacitance or magnetic fields as with conventional microphones. Since optical microphones do not react to electric and magnetic fields and are robust against heat and moisture, they are ideal for use in areas where conventional microphones are ineffective or dangerous to be used, such as industrial turbines or in magnetic resonance imaging (MRI) equipment environments.
An optical microphone includes generally a light source, an acoustic sensor such as a membrane having a reflective surface, optical transmitters such as optical fibers, and an optical detector. The light source emits a light beam, which is transmitted and guided by the transmitters to the acoustic sensor. The acoustic sensor is a sound-sensitive body that can detect acoustic pressure waves and reflect the light beam to the optical detector. Depending on the detected acoustic pressure waves, the acoustic sensor reflects the light beam with different properties, which are subsequently transformed into electric signals by the detector. The acoustic pressure waves can thus be analysed and measured.
Since the acoustic membrane in the optical microphone detects light beams rather than electric signals, the size of an optical microphone can be much smaller than the one of a conventional microphone. However, there are still demands for even smaller optical microphones to be used in specific conditions such as medical applications in human body.
In addition, since the oscillation pattern of the acoustic membrane is directly transmitted to the detector, the detection might be inaccurate and unreliable when the oscillation pattern of the membrane is fast and chaotic. In this case, it would be difficult to differentiate the real signals and the noise. There is a need to improve the signal-to-noise ratio (SNR) of the detection of an optical microphone.